A class of machines known as cold planers (e.g., Caterpillar PM565) are used to remove asphalt from road surfaces. A typical cold planer includes a plurality of drive tracks, a rotatable cutting drum, and a conveyor for transporting excavated asphalt away from the cutting drum. The cutting drum is equipped with a plurality of carbide teeth configured for milling a road surface when the drum is rotated. In operation, the cutting drum is typically rotated in a direction opposite from the direction of travel of the cold planer. Consequently, if the cold planer encounters a condition where the friction between the cutting drum and the road exceeds the friction between the tracks and the road, the machine may lurch backward. Such a condition is known as kickback.
To prevent kickbacks, a variety of kickback protection devices have been developed which are capable of sensing the backward movement of a cold planer and disabling the cutting drum of the cold planer. Current kickback protection devices are sensitive to small backward movements of the machine. This is a disadvantage when cutting concrete, cracked roads, or other surfaces which cause the machine to jerk slightly forward and backward. The backward jerking caused by rough road surfaces is not the same as a kickback and does not result in the cold planer being propelled backward any significant distance. However, this jerking often is enough to trip current kickback protection devices, thereby resulting in frequent false alarms and machine shut-downs. Frequent erroneous shut-downs are a nuisance to cold planer operators. Consequently, such operators often disable conventional kickback protection devices.
There currently is a need for a kickback protection device that allows for slight backwards movement of a cold planer without tripping a kickback alarm. There is also a need for a kickback protection device designed to allow an operator to adjust the sensitivity of the device to suit specific operating conditions. Furthermore, what is needed is a kickback device adapted to maintain contact with a road surface through discontinuities in the road and through changes in the elevation of the cold planer on which the device is mounted. Moreover, what is needed is a kickback protection device that also serves the function of sensing a relative elevation difference between a ground/road surface and a cutting plane of a cold planer. The present invention addresses these needs as well as other needs.